Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of transmitting the signals over long distances with very low loss.
Optical networks often employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmission capacity. In WDM and DWDM networks, a number of optical channels are carried in each fiber at disparate wavelengths. Network capacity is based on the number of wavelengths, or channels, in each fiber and the bandwidth, or size of the channels. Multiplexing can be used to increase the data rate in comparison to single stream transmission or to maintain the data rate but reduce the bandwidth requirements.
M-ary phase shift key modulation provides a shift in phase which can be used to multiplex two or more data streams. Likewise, polarization modulation provides a shift in polarization which can be used to multiplex two or more data streams. WDM and/or DWDM systems using polarization multiplexing and/or M-ary phase shift key may have increased spectral efficiency. For example, the wireless LAN standard, IEEE 802.11b-1999 uses a variety of phase shift key modulation schemes to increase efficiency. A system that incorporates both phase shift key modulation and polarization modulation may provide even more efficiency.